"If the car's brakes don't work due to a defect, you are not liable at all."
Morally perhaps but if you drive into the back of me because your brakes have a manufacturing fault I would still expect you to pay for the damage. The manufacturer may then be liable to you but that that is your business.
You'd don't expect the driver to pay, you just expect to be paid. Doesn't matter to you if it is OP, his insurance company or his car manufacturer. It does matter to the driver though, which is the reason of this discussion on liability.
If the car's brakes don't work due to a defect, you are not liable at all.
And if you show reasonable due diligence, that is regular maintenance, the same applies doubly so.
Beyond that, I've seen a lot of accidents, and none of them were the car's fault.
All were literally human error, or external factors. EG, deer leaping on to road, too many frogs on the road, etc